The heterogeneous electron transfer kinetics of biological molecules, horse heart cytochrome c, sperm whale myoglobin, and spinach ferredoxin, will be studied using spectroelectrochemical methods at surface modified electrodes. An electrochemical modification of electrodes with substituted 2,2' and 4.4' bipyridinium compounds, which was developed in this laboratory, yields a surface at which biological molecules undergo quasi-reversible rates of heterogeneous electron transfer. Ferrredoxin, myoglobin, and hemoglobin have been studied to date and these molecules exhibit drastically enhanced rate of heterogeneous electron transfer at modified electrode surfaces versus pristine electrode surfaces. The theory for spectroelectrochemically determining rates of heterogeneous electron transfer kinetic parameters was recently developed and experimentally verified in collaboration with H.N. Blount. This species selective method now provides a means of obtaining quantitative kinetic data for heterogeneous electron transfer by biological molecules when used in concert with the modified electrode surfaces described above. Since biological redox reactions often occur at heterogeneous interfaces, e.g. between membrane bound species and diffusing species, the proposed research should provide new information and insights into biological electron transfer processes. The molecules to be studied provide examples of heme type and iron-sulfur type biological redox molecules, cytochrome c and ferredoxin, respectively, and a biological molecule which does not function as a physiological redox species. Heterogeneous kinetic data for these molecules will be correlated with homogeneous electron transfer data previously reported from other laboratories.